In an initial double-blind randomized study with three parallel groups, 48 patients, mean age 49.6 years (32-65 years), with hypertension WHO I-II, were given bisoprolol in doses of 5, 10, and 20 mg. Bisoprolol is a new beta 1-selective beta-blocking agent with a plasma half-life of 10-12 h and without intrinsic sympathomimetic activity (ISA). After the initial 8 weeks, systolic (SBP) and diastolic blood pressure (DBP) and heart rate (HR) measured at rest and during exercise 24 h after last drug intake showed a significant decrease for all three parameters in all three treatment groups. There were no differences in efficacy between the 5 and 10 mg doses of bisoprolol, whereas 20 mg was significantly more effective than both 5 mg (p less than 0.01) and 10 mg (p less than 0.05). After 10 months of treatment with dose adjustments up or down, the reduction of SBP, DBP, and HR at rest and during exercise remained unchanged. One patient had an acute myocardial infarction (AMI) and died during the study; another patient had a car accident in which he got asphyxial cerebral lesions and could not complete the study. Twelve patients spontaneously expressed side effects of the kind normally seen in treatment with beta-blocking agents. Three of them complained of cold hands and feet, and one of them was unable to complete the study. The rest of the adverse effects were mild, and 45 patients completed the long-term study. Laboratory safety tests were normal, and there were no significant changes in the lipoprotein patterns (cholesterol, HDL cholesterol, and triglycerides).(ABSTRACT TRUNCATED AT 250 WORDS)